The invention relates to a method, a receiver and a mobile station for transmitting data in a radio communication system, in particular in TD/CDMA mobile radio systems.
International Publication No. WO 97/05707 describes a method for transmitting data between radio stations in a radio communication system, in which first signaling information items are superimposed with second or further information items at a transmitting end to form an aggregate signal, the aggregate signal is transmitted in a frequency channel, whereby it is possible to distinguish the first signaling information items and the second information items with the aid of individual fine structures, and a received signal is evaluated at a receiving end. International Publication No. WO 97/05707 also describes a receiver for a radio station, including a radio-frequency device for demodulating received signals, wherein first signaling information items and second or further information items, which can be distinguished with the aid of individual fine structures, are superimposed in the received signals to form an aggregate signal, and a coupling device for connecting the radio-frequency device to a signal-processing device.
In radio communication systems, messages (for example voice, image information or other data) are transmitted with the aid of electromagnetic waves through an air interface between transmitting and receiving radio stations (base station or mobile station, respectively). The emission of electro-magnetic waves is performed in that case by using carrier frequencies which are situated in a frequency band provided for the respective system. In the case of the GSM (Global System for Mobile Communication), the carrier frequencies are situated in the region of 900, 1800 or 1900 MHz. Frequencies in the frequency band of approximately 2000 MHz are provided for future mobile radio networks, for example the UMTS (Universal Mobile Telecommunication System) or other systems of the third generation.
The currently existing mobile radio system GSM (Global System for Mobile Communications) is a mobile communication system having a TDMA (Time Division Multiple Access) component for subscriber separation. User information items of the subscriber connections are transmitted in time slots in accordance with a frame structure. The transmission is performed in blocks. Organization channels (BCCH broadcast control channel) which are also known from the GSM mobile radio system are likewise matched to the time frame of the frame structure, for transmitting signaling and organization information items to all mobile stations in the respective radio cell. Those organization information items include details of the location area, the radio cell, the channel structure and of options which are supported inside the cell. Further signaling information items are transmitted in the down direction.
With the aid of the organization channel, which is emitted at maximum power, a mobile station undertakes performance measurements which permit statements to be made on the radio cell suitable for a connection set-up or handover. That organization channel is transmitted in a dedicated time slot in the frequency range of the user information.
German Patent DE 197 13 667 C1 discloses a radio communication system with TDMA/CDMA subscriber separation (Code Division Multiple Access), in which the organization information items are emitted as first signaling information items, likewise together with further information items, for example with user information items, in one frequency range. On one hand, the disadvantage of that solution resides in the additional interference which the organization channel entails for the user data channels. On the other hand, the user information items or further signaling information items also disturb the transmission of the first signaling information items. The range of the organization channel is also reduced.
It is accordingly an object of the invention to provide a method, a receiver and a mobile station for transmitting data in a radio communication system, which overcome the hereinafore-mentioned disadvantages of the heretofore-known methods and devices of this general type and which improve detection of further information items.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method for transmitting data between radio stations in a radio communication system, which comprises superimposing first signaling information items with second information items at a transmitting end to form an aggregate signal; transmitting the aggregate signal in a frequency channel, for distinguishing the first signaling information items and the second information items with the aid of individual fine structures; evaluating a received signal at a receiving end; initially reducing an influence of the first signaling information items on the second information items by a compensation calculation carried out with reference to the received signal; and subsequently detecting the second information items in the received signal already subjected to the compensation calculation.
With the objects of the invention in view, there is also provided a receiver for a radio station, comprising a radio-frequency device for demodulating received signals, the received signals having first signaling information items and second information items, to be distinguished with the aid of individual fine structures, superimposed therein to form an aggregate signal; a coupling device; a signal-processing device connected to the radio-frequency device by the coupling device, the signal-processing device including a device for reducing an influence of the first signaling information items on the second information items by a compensation calculation, and a detection device for the second information items; and the influence reducing device carrying out the compensation calculation before the detection device begins to detect the second information items.
With the objects of the invention in view, there is additionally provided a mobile station, comprising the receiver.
The interference affecting the further information items to be detected is reduced by the measure of compensating for the influence of the first signaling information items before detecting the further information items. The first signaling information items can be emitted without losses in quality at a higher transmission power, for example at the transmission power of the further information items, resulting in an increase in range.
It is thereby also possible for more remote radio stations, for example mobile stations in neighboring radio cells, to use the first signaling information items for performance measurement and cell selection. According to the invention, the transmission of the further information items need not be performed coherently with the first signaling information items. The transmission is admittedly performed in a common frequency band, that is to say with superimposition in terms of power, but there is no correlation between the signal components in the transmitted signal.
In accordance with another mode of the invention, the method operates particularly advantageously if the first signaling information items are emitted at the transmitting end with a lower level of directional selectivity than the further information items. In the case of a different directional selectivity, a channel estimation is carried out at the receiving end with the aid of training sequences embedded in the further information items.
The lower level of directional selectivity can be compensated by a higher process gain. The higher process gain can be implemented, for example, by the selection of a higher spread factor for the first signaling information items.
The greater spread factor for the first signaling information items is achieved according to an advantageous development by virtue of the fact that their symbols have a longer symbol duration than the symbols of the further information items. The symbol duration of the first signaling information items can be an integral multiple of the further information items. Consequently, the chips of all of the CDMA codes forming the fine structures can have one chip length (or an integral multiple thereof). As a consequence, a common clock can be used to produce the chips.
The greater process gain for the organization information items is advantageously achieved by using a significantly lower data rate than the data rate for the user information. This lower data rate is, for example, less than or equal to 1 kbit/s. The organization information items are thus limited to the most essential details, but these are transmitted in a highly interference-resistant manner. As soon as a mobile station is registered in a radio cell, the first signaling information items of the mobile station are known and can therefore be eliminated during the subsequent detection of the further information items.
In accordance with a further mode of the invention, the first signaling information items and the further information items are emitted at the transmitting end with approximately the same directional selectivity, and a channel estimation is carried out at the receiving end with the aid of the first signaling information items. Since the transmission channels are similar in this case for all information items, a single channel estimation suffices. This means a reduction in outlay in the case of the receiver. The further information items are advantageously transmitted at the transmitting end without training sequences with a lengthened data component. The data rate of the further information items can thereby be increased.
If an antenna diversity method is applied at the receiving end, it is advantageous to carry out the removal of the influence of the signaling information items for the received signals of each individual antenna element. The received signals which are thereby improved can thereupon be evaluated for the purpose of detecting the further information items with the aid of an algorithm for joint detection. The mutual influencing of the further information items is thereby also reduced.
The method according to the invention can advantageously be used for two alternative transmission methods. According to a first variant, the first signaling information items are emitted at the transmitting end in a continuous wave transmission, whereas the further information items are emitted in time slots using a TDMA transmission method. According to a second variant, the first signaling information items and the further information items are emitted at the transmitting end in time slots using a TDMA transmission method. It is thereby possible to implement the method according to the invention in a simple way in a radio communication system with the aid of the known TD/CDMA transmission method. However, it is also possible to emit all information items using continuous-wave transmission.
The influence of the first signaling information items is removed, for example, in such a way that a channel estimation is carried out for the first signaling information items, and channel coefficients are determined. A quantity is subtracted from the received signal. That quantity corresponds to the product of the channel coefficients and a known matrix of at least parts of the first signaling information items. In this case, the matrix is present in the receiving radio station. The channel coefficients are advantageously determined through the use of a Gauss-Markov estimation.
In order to further improve reception, it is advantageous to remove the influence of the first signaling information items on the basis of channel estimations at a plurality of instants. Error compensation is therefore performed for the channel estimation. A time interval over which the channel estimation is carried out can be set at the receiving end in accordance with the transmission conditions. Furthermore, it is advantageously possible to use adaptive channel estimation methods in the case of which the currently estimated channel coefficients are rated more highly than the channel coefficients previously estimated, which are likewise included in the compensation calculation.
According to an advantageous development of the invention, the frequency channel is a broadband channel, and the information items are spread with the aid of CDMA codes. The method according to the invention is therefore suitable, in particular, for broadband channels in which the information items can be transmitted with more resistance to interference.
In the case of TDMA/CDMA transmission methods, the invention is developed to the effect that, using a TDMA subscriber separation method, the further information items are transmitted in time slots with the aid of a known time pattern. This permits implementation in the existing GSM mobile radio network without the need to change the time pattern.
Error protection coding of the first signaling information items and the further information item can be carried out at the transmitting end for the purpose of further increasing the range. The error protection coding of the first signaling information item offers better protection than the error protection coding of the further information items.
This entails particular advantages if the first signaling information items have to be transmitted, for example, omnidirectionally as organization information items, with the result that no antenna gain is available for improved transmission.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a method, a receiver and a mobile station for transmitting data in a radio communication system, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.